Drilling and producing offshore oil and gas wells includes the use of offshore facilities for the exploitation of undersea petroleum and natural gas deposits. A typical subsea system for drilling and producing offshore oil and gas can include the installation of an electrical submersible pumping system (ESP) that can be used to assist in production.
Normally, when ESPs are used with wells, they are used during production to provide a relatively efficient form of “artificial lift” by pumping the production fluids from the wells. By decreasing the pressure at the bottom of the well bore below the pump, significantly more oil can be produced from the well when compared with natural production.
ESPs include both surface components (housed in the production facility or an oil platform) and sub-surface components found in the well. The surface components include the motor controller (which can be a variable speed controller) and surface cables and transformers. Subsurface components typically include the pump, motor, seal, and cables. Sometimes, a liquid/gas separator is also installed. The pump itself may be a multi-stage unit with the number of stages being determined by the operating requirements. Each stage includes a driven impeller and a diffuser that directs flow to the next stage of the pump. The energy to run the ESP pumpcomes from a high-voltage alternating-current source connected with the ESP pump via electrical cable from the surface.
Typically, for subsea structures, horizontal trees have been considered the best arrangement for supplying electricity to an ESP pump suspended on the production tubing. However, at least one problem exists with using a horizontal tree for supplying electricity to an ESP pump: if a horizontal tree is to be recovered for any reason, the tubing hanger must be recovered first, as it sits above or on the horizontal tree. This could be very costly to perform, and thus, a key reason why a more cost effective method is desirable. A tubing hanger recovery requires a very costly drilling rig since well pressure control and large bore access is mandatory. Tubing hanger recovery and successful re-completion of the downhole assembly involves significant risk.